"It's widely assumed that Austen was a perfect stylist - her brother Henry famously said in 1818 that 'everything came finished from her pen' and commentators continue to share this view today," the Oxford University English literature academic said.

"The reputation of no other English novelist rests so firmly on this issue of style, on the poise and emphasis of sentence and phrase, captured in precisely weighed punctuation.

"But in reading the manuscripts, it quickly becomes clear that this delicate precision is missing."

Sutherland said that Austen's unpublished manuscripts "unpick her reputation for perfection in various ways."

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"We see blots, crossings out, messiness - we see creation as it happens, and in Austen's case, we discover a powerful counter-grammatical way of writing. She broke most of the rules for writing good English," the academic added.

In particular, the "polished punctuation and epigrammatic style" typical of some of her novels is missing, suggesting someone else was "heavily involved" in editing her work, Sutherland said.

"Letters between Austen's publisher John Murray II and his talent scout and editor William Gifford, acknowledging the untidiness of Austen's style and how Gifford will correct it, seem to identify Gifford as the culprit," she added.

Austen, born in 1775, lived most of her life in Hampshire, southern England. She died in 1817, aged 41, from an unknown illness.

Her novels, published from 1811 onwards, include Sense and Sensibility, Pride and Prejudice, Mansfield Park, Emma, Northanger Abbey and Persuasion.

Murray was Austen's publisher for the last two years of her career, overseeing Emma, the second edition of Mansfield Park and Persuasion.

Sutherland's discoveries about the author's prose style came as part of a project to create a free online archive of all Austen's handwritten fiction manuscripts.

The archive is officially launched today at www.janeausten.ac.uk.

It will bring the manuscripts together in one place for the first time since 1845 when they were dispersed among family members under the terms of Austen's sister Cassandra's will.